This invention relates to a visual inspection and fault location system for millimeter waveguide and the like.
For certain fault conditions in installed millimeter waveguide, it is desirable to perform by remote control instrumentation a visual observation of a guide defect such as dielectric lining delamination, helix wire unwrap, welded coupling failure, etc. Video cameras have been designed which are small enough to be attached to a remote controlled self-propelled telemetry unit, termed a "long distance mouse" because it travels through buried waveguide. These video cameras typically use optics designed for the 16 millimeter movie picture format. Ideally, the lens system to use for this inspection purpose would be a "fisheye" lens with a viewing angle of at least 180.degree.. As a matter of fact, fisheye lenses of this type were designed initially for the remote inspection of pipe lines and casings associated with oil drilling rigs. All commercially available fisheye lenses with a 180.degree. or larger angle of view are expensive and, more importantly, too large in diameter to fit inside the WT4 millimeter waveguide (guide diameter is 60 mm). The cost of designing and producing a special fisheye lens for millimeter waveguide inspection is likely to be in the neighborhood of several hundred thousand dollars and thus would be prohibitive. Also, fisheye lenses suffer from image distortion, which makes images often difficult to interpret.